The handwritten letter, penned jointly by Vincent van Gogh and Paul Gauguin on cheap paper torn out of a school exercise book, speaks of friendship and hope. Written at a critical point in the careers of both men, it refers to dreams of founding a utopian community of brother artists, of a new artistic renaissance, and of paintings now recognised as masterpieces.

The reality was to be less idyllic. Shortly after the missive was sent, the pair quarrelled violently and in one of history's most notorious acts of self-mutilation, Van Gogh sliced off his right ear. It was an act that marked the Dutchman's final decline into madness and suicide.